Forum describes 25G backplane, standard

CUPERTINO, Calif.  Members of the Optical Internetworking Forum have successfully demonstrated a 25 Gbit/second backplane, more than twice the speed to today's typical systems. The milestone was reported at an open workshop hosted by the OIF that is drafting a standard for 25G interconnect.

Carriers have been demanding fast and efficient 100 Gbit Ethernet systems that need 25G chip-to-chip and backplane links. The OIF is using the workshop here to gather input on its 25G draft.

"The whole point of today is to get discussion going," said David Stauffer, a senior member of technology staff at IBM who chairs the OIF's physical and link layer working group writing the standard.

The work is already getting attention from Ethernet, Fibre Channel and Infiniband standards groups. The IEEE 802.3 may put out a call for interest soon for a set of 100G Ethernet standards based on four 25G links. Its work on 100G Ethernet today is typically based on ten 10G links.

The OIF's 25G demo used a simulation of serdes with non-return to zero signaling, decision feedback and other equalization techniques at both the receiver and transmitter. The simulated signaling was run over an actual board with novel materials and connectors from a company that requested to remain unnamed.

The backplane maker "thought it was something they could take into production, and IBM thinks it's feasible," said Stauffer.

The OIF's draft standard calls for a four-tap feed-forward equalizer in the transmitter at 800 to 1,200 Vppd. Board channels are restricted to no more than 25dB insertion loss across 30 inches and two connectors.

The result should take no more than 1.5 times the power of today's 10G links. "If we use more no one will buy it," Stauffer said.

OIF members such as IBM, LSI and Force10 have been working on 25G links since 2005. While their current demo seems promising, the group wants to make sure companies who have not been participating in their process understand the existing work and can provide feedback before a final spec is fixed.

The demand is clear.

""We need big, fat, intelligent pipes," said Hans-Martin Foisel, president of the OIF and a senior technologist at Deutsche Telekom."American carriers have publically stated they want 100G systems today, but my expectation is they will be deployed in about two or three years," he added.

The OIF has separate carrier and OEM working groups that are defining requirements for systems and their components. The groups are already looking to define their needs beyond 100G, Foisel said.